Following along as I'm planning out what to wear for 12 days in Iceland & London in early March....
My gut says it sounds like you'll be more apt to wear the skirts + tall boots than the skinnies, so go with that but pack a range of leggings -- fleece for colder weather, tights for warmer weather.
For just 6 days, with what sounds like not tourist-level walk all day walking, yes you may be able to get away with just the tall boots, which you've already thoroughly road tested. Perhaps just bring a second pair that works with skirts -- oxfords or ballet flats or booties -- they don't have to be all day shoes, just shoes to give you a break for a few hours if needed.
As for the scarves, I'm inclined to suggest adding a second, just to add interest, but the new one doesn't sound like "it." Perhaps you could just take one but make it a goal to purchase a second one there, as a souvenir of your trip?
As for bag... that one is tough! I'm in same boat, major dilemma. I am leaning towards take the Minkoff backpack, because it does leave room to stuff in hats/gloves/scarf/umbrella.... if I wasn't going to be outside walking around doing the touristy thing all day long, then I'd bring a smaller bag. Here's an idea: take the smaller crossover, but bring a packable lightweight tote?